1. Field of the Invention
The invention relates to a fuel injection device for use in an internal combustion engine.
2. Description of the Prior Art
For better comprehension of the description and claims, several terms will first be explained: The fuel injection device of the invention is embodied in stroke-controlled fashion. Within the scope of the invention, a stroke-controlled fuel injection device is understood to mean that the opening and closing of the injection opening is effected with the aid of a displaceable nozzle needle, on the basis of the hydraulic cooperation of the fuel pressures in a nozzle chamber and in a control chamber. A pressure drop inside the control chamber causes a stroke of the nozzle needle. The pressure at which fuel emerges from the nozzle chamber into a cylinder of an internal combustion engine is called the injection pressure, while the term system pressure is understood to mean the pressure at which fuel is available or kept on hand inside the fuel injection device. Fuel metering means furnishing a defined fuel quantity for injection. The term leakage is understood to mean a quantity of fuel that occurs in operation of the fuel injection device (such as a reference leakage or a control quantity) that is not used for injection and is pumped back to the fuel tank. The pressure level of this leakage can have a standing pressure, and the fuel is then subsequently depressurized to the pressure level of the fuel tank.
A stroke-controlled fuel injection device with a pressure booster has become known from German Patent Disclosure DE 199 10 970 A1. Each injection nozzle of a common rail system is assigned a hydraulic pressure booster, which enables both an increase in the maximum injection pressure to high pressures, such as pressures above 1800 bar, and the furnishing of a second injection pressure. By means of the pressure booster, the pressure storage chamber and the injection nozzle are subjected to a lower, permanent pressure level (rail pressure) than in conventional common rail systems and thus has a longer service life. The high-pressure pump is also subjected to less stress. The possibility exists of a well-meterable preinjection with low tolerances, by means of a low (unboosted) injection pressure. By switching over between injection pressures, a flexible shaping of the injection rate can be achieved, along with a plurality of preinjections and postinjections at high and low injection pressure, respectively.
To reduce the effort and expense in a fuel injection system with a pressure reservoir and a pressure booster, only a single valve is used to trigger the pressure booster and the nozzle needle. The present invention reduces the effort and cost of producing the valves and the effort and cost for the associated control electronics in the control unit. The disadvantage of the reduced flexibility of the injection course can be compensated for by suitable delay members. Adapting delay members makes it possible to adapt the behavior over time of the pressure buildup by the pressure booster to the demand presented by the engine.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings.